Fluorine removal by ion exchange

ABSTRACT

A method for removing fluorine gas from a selected environment comprises contacting the fluorine gas with water to generate a solution of hydrofluoric acid and contacting the solution of hydrofluoric acid with an ion exchange resin having an active state operative to exchange selected ions therein for fluoride ions in the solution. The apparatus ( 200 ) may include a dual resin setup ( 222, 223 ) such that one of the ion-exchange resin can be in the service cycle while the other of the ion-exchange resins undergoes the regeneration and rinse/refill cycles.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/168,962, filed Dec. 3, 1999, and U.S. Provisional Application No.60/177,827, filed Jan. 25, 2000.

FIELD OF THE INVENTION

The present invention generally relates to the removal and collection ofundesirable wastes produced as byproducts of industrial processes. Moreparticularly, the present invention is directed to converting fluorinegas in chemical vapor used in semiconductor manufacturing processes to adisposable form thereof. In particular, the present invention isdirected to a method and apparatus for use in removing and collectingfluorine that is produced in industrial processes. Additionally, thepresent invention includes a system using the method and apparatus ofthe present invention in industrial processes requiring the removal andcollection of fluorine.

BACKGROUND OF THE INVENTION

Semiconductor manufacturing processes generally involve the use ofChemical Vapor Deposition during processing of dielectrics and metals.Certain parts of the manufacturing process also etch semiconductorcomponents with chemical vapor, which typically consists ofperfluorinated compounds (PFCs) and fluorine gas. The steps of themanufacturing process are typically achieved by specific tools, whichare generally cleaned after a number of cycles. In many industrialprocesses, such as semiconductor manufacturing, some amounts of fluorinegas remain unutilized.

Fluorine gas is highly corrosive, and both elemental fluorine and thefluoride ion can be highly toxic. Accordingly, it is desirable to safelyand efficiently remove and properly dispose of fluorine and/or fluorideused in industrial processes, and in semiconductor manufacturingprocesses in particular.

Current technologies for fluorine removal focus on scrubbing thefluorine gas with simple air scrubbers to produce a constant bleed ofhydrofluoric acid (HF), which is generally sent to a manufacturingfacility's Acid Waste Neutralization (AWN) system for processing anddisposal. Because HF is a weak acid with a pK_(a) of 3.16, thetransformation of F₂ to HF is discouraged at low pH values. This becomesproblematic for scrubbers, as pH becomes the controlling mechanism forbleed volumes and consequently for concentration of HF. Further,increasing pH, such as by addition of alkali, poses further problemsbecause OF₂, an undesirable byproduct, can be produced in an alkalineenvironment in the presence of hypofluorous acid (HOF), which is alsoformed during the reaction of F₂ with water. Additionally, despiteoperating at maximum allowable concentrations of HF in the scrubber, theHF reaching the AWN is generally too dilute for optimal operation offluorspar (CaF₂) precipitation systems. Further, large amounts ofchemicals are consumed in conventional CaF₂ precipitation systems.Additionally, the sludge volume is very high due to the high level ofhydration, requiring excessive CaF₂ sludge hauling.

Accordingly, there remains a need to provide a new and improved methodand apparatus for removing and collecting fluorine and/or fluoride.There further remains a need for a system for removing fluorine whichhas a low operating cost and which generates a concentrated end productthat can be hauled away economically. The present invention is directedto meeting these needs.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a new and usefulmethod for removing fluorine gas from a selected environment.

It is another object to provide a low operating cost method for removingand disposing of undesirable byproducts of industrial processes.

It is yet another object of the present invention to provide a new anduseful apparatus for removing and collecting fluorine and/or fluoride inselected manufacturing processes.

A still further object of the present invention is to provide anapparatus which generates a concentrated fluoride end-product that canbe economically disposed of and that does not require excessive sludgehauling.

Yet another object of the present invention is to provide a system thatremoves fluorine gas from industrial manufacturing processes andprovides a disposable end-product thereof.

According to the present invention, a method is provided for removingfluorine gas from a selected environment. The method comprises the stepsof contacting the fluorine gas from the environment with a selectedquantity of water, thereby to generate a solution of hydrofluoric acid,and contacting the solution of hydrofluoric acid with an ion-exchangeresin having an active state operative to exchange selected ions thereinfor fluoride ions in the solution when in contact therewith. Acontinuous stream of water may be contacted with a continuous stream offluorine gas, such as by injecting the fluorine gas into the water.Where the selected environment includes silica particles, the method mayinclude the step of filtering the solution of hydrofluoric acid througha porous strong base anion resin thereby to remove silica particlesdisposed in the solution.

The step of contacting the solution with the ion-exchange resin may beaccomplished by passing the solution of hydrofluoric acid through aresin vessel in which the ion-exchange resin is disposed. Theion-exchange resin may be a weak-base anion exchange resin or a strongbase anion exchange resin, and is preferably a crosslinkedpoly-4-vinylpyridine resin or a derivative thereof, and more preferablya Reillex™ 402 or Reillex™ 425 resin. The method may include doping theion-exchange resin with an electron donor catalyst, such as palladium ortitanium. The step of doping may be accomplished by contacting theion-exchange resin with a salt of the catalyst and thereafter contactingthe ion-exchange resin with an oxidizing agent.

The ion-exchange resin may be capable of chemically shifting between theactive state and an exhausted state operative to exchange the fluorideions in the ion-exchange resin for the selected ions contained in aregenerant solution, such as an ammonium hydroxide solution, when incontact therewith, wherein the method may include the step ofregenerating the ion-exchange resin by contacting the ion-exchange resinwith the regenerant solution thereby to form a selected regenerant wasteproduct containing the fluoride ions, such as ammonium fluoride. Themethod may include the step of rinsing the ion-exchange resin with arinse solution, such as de-ionized water, after the step of regeneratingthe ion-exchange resin. The rinse solution may thereafter be used toreplenish the regenerant solution. The regenerant waste product may becollected in a storage vessel.

The solution of hydrofluoric acid may be cooled, such as by use of aheat-exchange apparatus, prior to the step of contacting the solutionwith the ion-exchange resin. A reducing agent may be added to thesolution of hydrofluoric acid prior to the step of contacting thesolution of hydrofluoric acid with the ion-exchange resin.

The present invention also relates to an apparatus for use in removingfluorine from a selected environment. The apparatus comprises an inletin communication with the selected environment and operative to providefluorine gas therefrom, a conduit in communication with the inlet andadapted to receive fluorine gas therefrom and operative to transport anaqueous solution therethrough, a resin vessel in fluid communicationwith the conduit and operative to receive the aqueous solutiontherefrom, and an ion-exchange resin disposed in the resin vessel andadapted to contact the aqueous solution. The ion-exchange resin has anactive state operative to exchange selected ions therein for fluorideions in the aqueous solution when in contact therewith.

The inlet may include an injector, such as a vacuum pump or an eductor,that is operative to inject the fluorine gas into the conduit. The resinvessel may receive the aqueous solution in a fluid compartment thereofand further include a chamber proximate to the fluid compartment that issized and adapted to permit a gas, such as N₂, disposed in the aqueoussolution to separate therefrom and enter the chamber, which may be incommunication with a scrubber operative to receive the gas from thechamber.

The ion-exchange resin for use in the apparatus is similar or identicalto that for use in the method of the invention. When the ion-exchangeresin is capable of chemically shifting between the active state and theexhausted state, the apparatus may include a regenerant source vesseladapted to receive the regenerant solution. The regenerant source vesselis in fluid communication with the resin vessel and operative toselectively provide the regenerant solution to the resin vessel. A rinsesolution source in fluid communication with the resin vessel mayselectively provide a rinse solution to the resin vessel. A regenerantwaste outlet in fluid communication with the resin vessel may be adaptedto receive therefrom a regenerant waste solution containing fluorideions. A regenerant waste vessel may be further in fluid communicationwith said regenerant waste outlet to receive a selected quantity of theregenerant waste solution. A heat-exchange apparatus may be disposedproximate to the conduit and operative to transfer thermal energy awayfrom the conduit. A reducing agent source in communication with theconduit may selectively introduce a reducing agent into the conduit,such as via a positive displacement metering pump.

The present invention also relates to an apparatus for use in removingfluorine from a selected environment that comprises first and secondion-exchange resins disposed in respective first and second resinvessels. A valve system includes a plurality of valves associated with aplurality of fluid pathways interconnecting selected ones of an inlet, aconduit, the first and second resin vessels, a regenerant source vessel,a rinse solution source and a regenerant waste outlet. The valve systemincludes various valve states permitting fluid flow. A controller may beoperative to move the valve system into its respective states, and a pHmonitor may generate a signal when the aqueous solution reaches a targetpH value.

The present invention further relates to an apparatus for use inremoving fluorine from a selected environment, comprising an inletoperative to provide fluorine gas from the environment to the resinvessel, in which is disposed an ion-exchange resin containing a selectedvolume percentage of water. The ion-exchange resin exchanges selectedions therein for fluoride ions generated by contact of the fluorine gaswith the ion-exchange resin having the volume percentage of water. Aheat-exchange apparatus may be disposed proximate to the resin vessel.

Finally, the present invention is directed to an apparatus for use inremoving fluorine from a selected environment, comprising a scrubber incommunication with the inlet and adapted to receive fluorine gastherefrom. The scrubber is operative to contact the fluorine gas withwater thereby to form a solution of hydrofluoric acid. The resin vesselreceives the solution from the scrubber, and the ion-exchange resindisposed in the resin vessel exchanges selected ions in the ion-exchangeresin for fluoride ions in the solution when in contact therewith.

These and other objects of the present invention will become morereadily appreciated and understood from a consideration of the followingdetailed description of the exemplary embodiment of the presentinvention when taken together with the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a diagrammatic view of the method according to the presentinvention;

FIG. 1 b is a diagrammatic view of optional steps of the method of FIG.1 a;

FIG. 2 a is a diagrammatic view of a first embodiment of an apparatusaccording to the present invention, showing the service cycle inoperation;

FIG. 2 b is a diagrammatic view of the apparatus according to FIG. 2 a,showing a regeneration cycle in operation;

FIG. 2 c is a diagrammatic view of the apparatus of FIGS. 2 a and 2 b,showing a rinse/refill cycle in operation;

FIG. 3 a is a diagrammatic view of a second embodiment of an apparatusaccording to the present invention, showing a service cycle of a firstresin and a regeneration cycle of a second resin;

FIG. 3 b is a diagrammatic view of the apparatus shown in FIG. 3 a,showing a service cycle of the first resin and a rinse/refill cycle ofthe second resin;

FIG. 3 c is a diagrammatic view of the apparatus of FIGS. 3 a and 3 b,showing a service cycle of the second resin and a regeneration cycle ofthe first resin;

FIG. 3 d is a diagrammatic view of the apparatus of FIGS. 3 a through 3c, showing a service cycle of the second resin and a rinse/refill cycleof the first resin;

FIG. 4 is a diagrammatic view of a third embodiment of an apparatusaccording to the present invention; and

FIG. 5 is a diagrammatic view of a fourth embodiment of an apparatusaccording to the present invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The present invention provides an efficient method, apparatus and systemfor removing fluorine gas from industrial manufacturing processes. Itshould be understood, however, that the present invention may beutilized in virtually any situation in which fluorine and/or fluoridecollection and removal is desirable.

Generally, fluorine in use in semi-conductor manufacturing processes ismixed in a vacuum pump with a carrying gas, such as N₂ or other inertgases, preferably in a ratio of 40 liters of N₂ per 1.5 liters F₂. Inthe method of the present invention, this gas mixture is injected intoan aqueous solution thereby to generate HF, which is believed to occuraccording to the following reactions I and II:F₂+H₂O

HOF+HF  (I)HOF+H₂O

H₂O₂+HF  (II)

Further, HF is a weak acid, with a pK_(a) of 3.16. Accordingly, at lowpH values, the transformation of F₂ to HF is discouraged. Adjustment ofpH, such as by addition of alkali, poses the additional problem ofgenerating undesirable OF₂ which can be produced under alkalineconditions according to reaction III as follows:F₂+HOF

OF₂+HF  (III)Accordingly, in order to operate an optimum F₂ removal/abatement deviceit is desirable to reduce the HOF, such as by adding a reducing agent,and to keep a pH environment preferably of between 5 and 7. Further,because the reaction of F₂ with water may be exothermic, it is furtherdesirable to dissipate heat generated thereby, such as through the useof a heat exchange device.

As shown in FIG. 1 a, then, the general method 10 of the presentinvention comprises service cycle 11, which includes injecting F₂ gas12, preferably provided by an inlet 14, into a water stream 16, which ispreferably a recirculating, or closed-loop, stream. A closed loop allowsfor higher flow rates and accordingly more efficient operation. HF 18generated by the reaction of F₂ with water is passed through anion-exchange resin 20, which is preferably disposed in a resin vessel22. HF that contacts the ion-exchange resin 20 undergoes ion-exchangesuch that fluoride ions, F⁻, are captured by ion-exchange resin 20.Alternatively, F₂ gas 12 may be injected directly into contact withion-exchange resin 20 when the resin is of a type which has a high watervolume percentage and is stable to oxidation by F₂. In this case, F₂ gas12 reacts with the moisture in the ion-exchange resin 20, thereby togenerate HF 18 which undergoes ion-exchange with the functional groupsof ion-exchange resin 20.

The preferred ion-exchange resin is a crosslinked poly-4-vinylpyridineresin and derivatives thereof, such as those manufactured by ReillyIndustries, Inc., 1500 South Tibbs Avenue, Indianapolis, Ind., under thetradenames Reillex™ 402 and 425. The pyridine functional groups of theseresins are highly resistant to attack by oxidizing and reducing agentsand have an unusually high capacity for HF. Further, these resins resistoxidation by hydrogen peroxide, H₂O₂, postulated to be formed by thereaction of HOF and H₂O. It should be understood, however, that otherion-exchange resins may be utilized in accordance with the presentinvention. In particular, the present invention contemplates resins witha weak base anion functionality, such as those having tertiary amines asmain functional groups and either styrene or acrylic backbones.Additionally, the present invention contemplates resins having a strongbase anion functionality, such as those having quaternary amines as mainfunctional groups and either styrene or acrylic backbones. Exemplaryweak base anion and stong base anion resins include those manufacturedby Purolite®, located in Bala Cynwyd, Pa., such as the A-860, A-845,A-100, A-870, A-600, A-510, A-500, A-500P, A-400, A-300, A-300E, A-200,and A-850 Purolite® ion-exchange resins.

Additionally, the present invention contemplates the use of resins whichhave been doped, or impregnated, with a catalyst to increase the rate ofconversion of F₂ to F⁻. The use of a catalyst may be desirable when thesystem conditions favor F₂ in the F₂

2F⁻ equilibrium, such as under low pH, for example, or when a scrubberis not present in the system. The preferred catalyst is an electrondonor, such as palladium or titanium metal, which accelerates theconversion of fluorine to fluoride. A resin may be doped with such acatalyst by, for example, contacting the resin with a palladium chloridesalt solution and thereafter contacting the resin with an oxidizerthereby to precipitate the palladium metal in stoichiometric amounts. Itshould be appreciated that resins resistant to oxidation, such as thecrosslinked poly-4-vinylpyridine resins and derivatives thereofdiscussed above, are particularly suitable for catalyst doping by thismethod.

It should be appreciated that other types of media may be substitutedfor the ion-exchange resin of the present invention. In particular, acidabsorption or neutralizing media that sacrificially hydrates orneutralizes hydrofluoric acid, such as limestone or other calciumcompounds, may be employed. However, such media are less preferredrelative to media such as ion-exchange resins, which may be efficientlyregenerated.

When an ion-exchange resin is utilized, the method of the presentinvention may additionally include a regeneration cycle 24 and arinse/refill cycle 34, as shown in FIG. 1 b. The regeneration cycle 24includes providing a regenerant solution 26, preferably from aregenerant source vessel 28. Regenerant solution 26, which is preferablyammonium hydroxide, NH₄OH, is passed into resin vessel 22 and intocontact with ion-exchange resin 20. Ion-exchange resin 20 undergoesion-exchange with regenerant solution 26 thereby to form a regenerantwaste 30 containing concentrated fluoride ion, F⁻. When NH₄OH is used asthe regenerant solution 26, regenerant waste 30 contains NH₄F salt.Regenerant waste 30 is then passed to waste outlet 32, wherebyregenerant waste 30 may be either collected, such as in a dedicatedcontainer, or sent down a dedicated collection drain.

The rinse/refill cycle 34 includes providing a rinse solution 36,preferably de-ionized water, from a rinse source 38 such as a waterinlet. Rinse solution 36 is passed through resin vessel 22 and incontact with ion-exchange resin 20, thereby to rinse any remainingregenerant solution 26 from resin vessel 22. Regenerant rinse solution40 formed by rinsing resin vessel 22 may then be passed to regenerantsource vessel 28, thereby to refill regenerant source vessel 28 with anaqueous solution whose concentration may thereafter be adjusted, such asby addition of concentrated NH₄OH to form the desired regenerantsolution 26.

The method 10 of the present invention may additionally include one ormore of the steps of cooling the water stream 16 to dissipate heatgenerated by the reaction of F₂ with water, monitoring theoxidation-reduction potential of water stream 16, adding a reducingagent to water stream 16 to assure decomposition of HOF formed duringthe reaction of F₂ with water, removing carrying gases provided alongwith F₂ gas 12 by inlet 14, monitoring pH for an indication thation-exchange resin 22 is exhausted, signaling for the beginning ofregeneration cycle 24, monitoring the concentration of regenerantsolution 26 and adjusting the concentration of regenerant solution 26 toregeneration levels, such as by pumping concentrated solution intoregenerant source vessel 28. In the case where F₂ gas 12 is pumpeddirectly into resin vessel 22, the method may include a further step ofhydrating ion-exchange resin 20 during service cycle 11, such as byproviding de-ionized water to resin vessel 22 to replace water used inreaction with F₂, or by providing moisture, such as in vapor form, toresin vessel 22.

A general embodiment of the apparatus 100 according to the presentinvention is shown in FIGS. 2 a-2 c. Here, apparatus 100 includes inlet114, preferably a vacuum pump or eductor, resin vessel 122 havingion-exchange resin 120 disposed therein, regenerant source vessel 128having regenerant solution 126 disposed therein, rinse source 138operative to provide a rinse solution, and waste outlet 132, here shownas a container adapted to receive regenerant waste 130. Inlet 114, resinvessel 122, regenerant source vessel 128, rinse source 138, and wasteoutlet 132 are fluidly connected by conduit 142, which is adapted toreceive a water stream. Pumps 146 and 148 are disposed in conduit 142,and each have an on state wherein they are operative-to pump fluidthrough conduit 142 and an off state wherein they do not pump fluid.Valves 150, 152, 154, 156, 158, 160 and 162 are disposed in conduit 142and are operative to move between a closed state preventing fluid flowtherethrough and an open state allowing fluid flow therethrough.

FIG. 2 a shows the service cycle for apparatus 100. Here, F₂ gas 112 isinjected from inlet 114 into water stream 116, which is a recirculating,or closed-loop, stream. Pump 146 is operative to pressurize andcirculate water stream 116 in conduit 142. Valves 150 and 162 are open,while the remaining valves are closed. HF laden water in water stream116 flows through resin vessel 122 where it undergoes ion-exchange withion exchange resin 120. Preferably, water stream 116 flows through resinvessel 122 in an up-flow direction, creating an expanded, or fluidized,resin bed. Carrying gas 164, such as N₂, is removed at top of resinvessel 122 which has a free volume 165 capable of allowing carrying gas164 to separate from the water stream 116, where it can then be directedto a location for further processing, such as by a scrubber.

When ion-exchange resin 120 is at full capacity of F⁻, a regenerationcycle begins as shown in FIG. 2 b. Here, valves 150 and 162 are closedand pump 146 is turned off. Preferably, inlet 114 is also closed orturned off as appropriate. Valves 160, 152 and 154 are opened and pump148 is turned on. Regenerant solution 126, preferably ammoniumhydroxide, is pumped from regenerant source vessel 128 and through resinvessel 122 which undergoes ion-exchange with ion-exchange resin 120,thereby to produce regenerant waste 130. When ammonium hydroxidesolution is used as the regenerant solution 126, ammonium fluoridesolution is formed as the regenerant waste 130 resulting fromregeneration of ion-exchange resin 120. The concentration, as well asrate of flow through resin vessel 122, of regenerant solution 126 ispreferably adjusted according to the concentration of regenerant waste130 that is desired. Preferably, regenerant waste 130 is a concentratedstream of ammonium fluoride that is easily disposed of without requiringexcessive sludge hauling.

Once ion-exchange resin 122 has been regenerated, a rinse cycle begins,as shown in FIG. 2 c. Here, valves 160 and 154 are closed and valves 156and 158 are opened, while pump 148 is turned off. Rinse solution 136,provided by rinse source 138, passes through resin vessel 122 to rinseany remaining regenerant solution 126 therefrom. Regenerant rinsesolution 140 then flows to regenerant source vessel 128, whereregenerant rinse solution 140 may be recycled to form a new regenerantsolution 126, such as by adding concentrated regenerant 167, preferablyammonium hydroxide, to regenerant source vessel 128 until a desiredregeneration concentration of regenerant solution 126 is achieved. Tothe extent understood by the ordinarily skilled artisan, a concentrationmonitor/control may be used to automatically adjust the concentration ofNH₄OH to regeneration levels by pumping concentrated solution toregenerant source vessel 128 as desired.

Once the rinse/refill cycle has completed, valves 152, 156 and 158 areclosed and valves 150 and 162 are opened, pump 146 is turned on, and ifnecessary inlet 114 is turned on or opened as appropriate, thereby tobegin the service cycle again.

The various on/off and open/closed states of valves and pumps during theoperation cycles for apparatus 100 is summarized in Table 1 below:

TABLE V Service Regeneration Rinse/Refill Cycle Cycle Cycle Pump 146 ONOFF OFF Pump 148 OFF ON OFF Valve 150 OPEN CLOSED CLOSED Valve 152CLOSED OPEN OPEN Valve 154 CLOSED OPEN CLOSED Valve 156 CLOSED CLOSEDOPEN Valve 158 CLOSED CLOSED OPEN Valve 160 CLOSED OPEN CLOSED Valve 162OPEN CLOSED CLOSED

A more preferred embodiment of the present invention is shown in FIGS. 3a-3 d. Here, apparatus 200 includes a dual resin setup, wherein twoion-exchange resins are utilized such that one of the ion-exchangeresins can be in the service cycle while the other of the ion-exchangeresins undergoes the regeneration and rinse/refill cycles. Thus, itbecomes unnecessary to interrupt the fluorine removal/abatement process,because a service cycle can be continuously performed by the apparatus.

Apparatus 200 includes a vacuum pump 214, which is operative to supplyF₂ gas 212 to a conduit 242 which interconnects various components ofthe apparatus 200. Preferably, a heat exchanger 268 is disposed inthermal communication with conduit 242 immediately downstream ofjuncture 270 where F₂ gas 212 is injected into a water stream 216circulating through conduit 242. Additionally, apparatus 200 preferablyincludes a reducing agent source 272 in fluid communication with conduit242 and operative to provide a reducing agent 274 which is capable ofreducing HOF which may be formed by the reaction of F₂ and water. To theextent understood by the ordinarily skilled artisan, the addition ofreducing agent 274 from reducing agent source 272 into water stream 216is preferably controlled by an oxidation-reduction potential (ORP)monitor, which signals for reducing agent 274 to be pumped from reducingagent source 272 when an oxidation-reduction potential is detected. Amixer 276 is also preferably provided to optimally mix reducing agent274 into water stream 216. It should be understood that the presentinvention contemplates the use of integrated heat-exchangers and mixersthat may be available in the art, such that heat exchanger 268 and mixer276 may be disposed in one apparatus. Additionally, a pH monitor 278 ispreferably provided, whereby the pH monitor is capable of monitoring thepH of the water stream 216 and operative to provide a signal when the pHdecreases below a selected threshold.

First resin vessel 222 and second resin vessel 223 are provided in fluidcommunication with conduit 242, and each resin vessel containsion-exchange resin 220 and 221, respectively. Rinse source 238 isfurther in fluid communication with conduit 242, and is operative toprovide de-ionized water 236. Regenerant source vessel 228 is operativeto provide dilute ammonium hydroxide 226. Waste outlet 232 is operativeto receive ammonium fluoride regenerant waste 230 resulting fromregeneration of either of ion-exchange resins 220 or 221.

Pumps 244, 246 and 248 are disposed in conduit 242 and are operative inan on state to pump fluid through conduit 242. It should be understoodthat pump 244 may be unnecessary if pump 246 provides sufficientcirculation through conduit 242. Valves 250 through 263 are disposed inconduit 242 and are operative to move between a closed state preventingfluid flow therethrough and an open state allowing fluid flowtherethrough.

As shown in FIGS. 3 a and 3 b, first resin vessel 222 can undergo aservice cycle while second resin vessel 223 undergoes both aregeneration cycle and a rinse/refill cycle. In particular, as shown inFIG. 3 a, pumps 244, 246 and 248 are turned on, valves 250, 253, 255,261 and 262 are opened and valves 251, 252, 254, 256, 257, 258, 259, 260and 263 are closed thereby to work a service cycle in first resin vessel222 and a regeneration cycle in second resin vessel 223. With respect tothe service cycle of first resin vessel 222, F₂ gas 212 from vacuum pump214 is injected into water stream 216 which circulates through firstresin vessel 222 and undergoes ion-exchange with ion-exchange resin 220.Carrying gas, such as N₂ may be removed at free volume 265.Concurrently, dilute NH₄OH 226 from regenerant source vessel 228 ispumped by pump 248 through resin vessel 223 thereby to regenerateion-exchange resin 221 to form NH₄F regenerant waste 230 which is sentto waste outlet 232.

As shown in FIG. 3 b, once ion-exchange resin 221 is regenerated, arinse/refill cycle begins on second resin vessel 223, while the servicecycle continues on first resin vessel 222. Here, pump 248 is turned off,valves 257 and 259 open and valves 255 and 261 close. De-ionized water236 from rinse source 238 is passed through second resin vessel 223thereby to rinse away any excess NH₄OH and to form regenerant rinsesolution 240 which is passed to regenerant source vessel 228 for reusein forming the NH₄OH regenerant solution 226. Concentrated NH₄OH 267 maybe added to regenerant source vessel 228 to adjust the concentration ofNH₄OH regenerant solution 226 as desired.

Once the rinse/refill cycle has completed, valves 259, 253 and 257 areclosed and the service cycle continues on first resin vessel 222 untilion-exchange resin 220 is exhausted, as indicated by a signal from pHmonitor 278 when the pH of water stream 216 declines below a selectedthreshold thereby indicating that HF is no longer undergoingion-exchange with ion-exchange resin 220.

At this time, as shown in FIGS. 3 c and 3 d, second resin vessel 223undergoes a service cycle while first resin vessel 222 undergoesregeneration and rinse/refill cycles. In particular, as shown in FIG. 3c, pumps 244, 246 and 248 are turned on, valves 251, 252, 254, 260 and263 are opened and valves 250, 253, 255, 256, 257, 258, 259, 261, and262 are closed. With respect to the service cycle through second resinvessel 223, F₂ gas from vacuum pump 214 is injected into water stream216 which circulates through second resin vessel 223 thereby undergoingion-exchange with ion-exchange resin 221. Carrying gas such as N₂ can beremoved at free volume 266. First resin vessel 222 undergoesregeneration as dilute NH₄OH is pumped by pump 248 from regenerantsource vessel 228 through first resin vessel 222 thereby undergoingion-exchange with ion-exchange resin 220 to form NH₄F regenerant waste230 which is sent to waste outlet 232.

As shown in FIG. 3 d, once ion-exchange resin 220 is regenerated, pump248 is turned off, valves 254 and 260 are closed and valves 256 and 258are opened. Second resin vessel 223 continues undergoing a servicecycle. De-ionized water 236 from rinse source 238 passes through firstresin vessel 222 thereby to rinse any excess NH₄OH therefrom. Theregenerant rinse solution 240 is then passed to regenerant source vessel228 where it is recycled for use in NH₄OH regenerant solution 226, theconcentration of which may be adjusted by addition of concentratedammonium hydroxide 267.

Once rinse/refill cycle has completed, valves 258, 252 and 256 areclosed and the service cycle continues on second resin vessel 223 untilion-exchange resin 221 is exhausted, as indicated by a signal from pHmonitor 278 when the pH of water stream 216 declines below a selectedthreshold thereby indicating that HF is no longer undergoingion-exchange with ion-exchange resin 220. At this point, a service cycleon first resin vessel 222 and a regeneration cycle on second resinvessel 223 begins again as shown in FIG. 3 a.

The various on/off and open/closed states of valves and pumps during theoperation cycles for apparatus 200 is summarized in Table 2 below:

TABLE 2 First resin First resin Second Second service service resinresin cycle/ cycle/ service service second second cycle/firstcycle/first resin regen. resin rinse resin regen. resin rinse cyclecycle cycle cycle Pump 244 ON ON ON ON Pump 246 ON ON ON ON Pump 248 ONOFF ON OFF Valve 250 OPEN OPEN CLOSED CLOSED Valve 251 CLOSED CLOSEDOPEN OPEN Valve 252 CLOSED CLOSED OPEN OPEN Valve 253 OPEN OPEN CLOSEDCLOSED Valve 254 CLOSED CLOSED OPEN CLOSED Valve 255 OPEN CLOSED CLOSEDCLOSED Valve 256 CLOSED CLOSED CLOSED OPEN Valve 257 CLOSED OPEN CLOSEDCLOSED Valve 258 CLOSED CLOSED CLOSED OPEN Valve 259 CLOSED OPEN CLOSEDCLOSED Valve 260 CLOSED CLOSED OPEN CLOSED Valve 261 OPEN CLOSED CLOSEDCLOSED Valve 262 OPEN OPEN CLOSED CLOSED Valve 263 CLOSED CLOSED OPENOPEN

A third embodiment of apparatus 300 is shown in FIG. 4. Here, service,regeneration and rinse/refill cycles operate similarly to the dual resinembodiment of FIGS. 3 a-3 d. FIG. 4 shows operation that corresponds toFIG. 3 a for the second embodiment of the apparatus, showing a servicecycle of first resin vessel 322 having ion-exchange resin 320 disposedtherein, and a regeneration cycle of second resin vessel 323 havingion-exchange resin 321 disposed therein. However, in this embodiment,during a service cycle of one of resin vessels 322 or 323, F₂ gas 312 isinjected from vacuum pump 314 directly into the resin bed of one or theother of ion-exchange resins 320 and 321, which each contain a volumepercentage of water of preferably approximately 42%. Again, thepreferred resin is a resin containing pyridine functional groups, suchas the crosslinked poly-4-vinylpyridine resins manufactured by Reilly.The pyridine resins are very stable such that F₂ generally will not hurttheir structure by oxidation.

As shown in FIG. 4, outlets 315 and 317 of vacuum pump 314 are attachedto the bottom of each of resin vessels 322 and 323, respectively, andvalves 350 and 351 direct F₂ gas 312 to either resin vessel. In thisembodiment, there is sufficient water in the ion-exchange resins 320 and321, respectively, for the reaction of F₂ and water that forms HF totake place. Preferably, cooling jackets 380 and 381 are respectivelydisposed proximate to resin vessels 322 and 323, thereby to dissipateany heat generated by the reaction of F₂ and water. Again, excesscarrying gas, such as N₂, may be removed at the free volumes 365 and 366disposed in resin vessels 322 and 323 respectively.

The ion-exchange resins 320 and 321 will become rehydrated during theirrespective regeneration cycles, given that the regeneration cycle is anaqueous cycle. However, if a selected type of resin containsinsufficient water for the HF reaction to take place until the resin isexhausted with F⁻, it may be necessary to provide a separate rehydrationcycle to either of ion-exchange resins 320 and 321 during theirrespective service cycles by providing de-ionized water 336 from rinsesource 338 through valves 358 or 359. Alternatively, moisture may beinjected in vapor form from an external source into resin vessels 322and 323 during their respective service cycles, thereby to providesufficient water for the reaction.

The various on/off and open/closed states of valves and pumps during theoperation cycles for apparatus 300 is summarized in Table 3 below:

TABLE 3 First resin First resin Second Second service service resinresin cycle/ cycle/ service service second second cycle/firstcycle/first resin regen. resin rinse resin regen. resin rinse cyclecycle cycle cycle Pump 348 ON OFF ON OFF Valve 350 OPEN OPEN CLOSEDCLOSED Valve 351 CLOSED CLOSED OPEN OPEN Valve 352 CLOSED CLOSED OPENOPEN Valve 353 OPEN OPEN CLOSED CLOSED Valve 354 CLOSED CLOSED OPENCLOSED Valve 355 OPEN CLOSED CLOSED CLOSED Valve 356 CLOSED CLOSEDCLOSED OPEN Valve 357 CLOSED OPEN CLOSED CLOSED Valve 358 CLOSED CLOSEDCLOSED OPEN Valve 359 CLOSED OPEN CLOSED CLOSED Valve 360 CLOSED CLOSEDOPEN CLOSED Valve 361 OPEN CLOSED CLOSED CLOSED

It should be appreciated that in this embodiment, it is possible toremove the T-shaped portion of conduit 342 shown in FIG. 4 that includesvalves 353, 355 and 357, such that the apparatus only utilizes—for theregeneration and rinse/refill cycles of both resin vessels—the T-shapedportion of conduit 342 that includes valves 352, 354 and 356.

As shown in FIG. 5, a fourth embodiment of the apparatus 400 accordingto the present invention may be seen as an attachment to existingconventional scrubbers, such as are currently used by the semi-conductormanufacturing industry. Here, the F₂ gas 412, again typically mixed witha 40:1 ration of N₂, would be brought into a scrubber 482, thereby togenerate HF by reaction with water. The water stream 416 from thescrubber is then cooled with heat exchanger 468, and a reducing agent474 from reducing agent source 472 is injected into water stream 416 toassure decomposition of HOF, and further mixing may be provided by mixer476. Operation of the service, regeneration and rinse/refill cycles ofthe apparatus 400 are similar to that discussed with respect to theapparatus 200 of FIGS. 3 a-3 d. Here, it should be noted that resinvessels 422 and 423 need not include any free volume for removingcarrying gases such as N₂, given that such gases 464 are removed byscrubber 482 and can be transported for further processing. A closedloop operation of water stream 416 is preferred, which allows for higherflow rates through the scrubber 482 and accordingly more efficientscrubbing.

In all embodiments of the present invention, it may desirable to removeany SiO₂ or other compounds of silica in the waste stream. That is,since HF in the semiconductor industry is used extensively for siliconwafer etching, and is also a product of the scrubbing of excess F₂ gasin the chamber clean process, there is generally SiO₂ and other silicacompounds in the waste stream. Due to the low pH, these compounds formgelatinous solids, or colloidal silica, generally in concentrations of300-400 ppm. Such particles are generally difficult to remove usingconventional filtration methods. Accordingly, to remove such silicaparticles in the waste stream, the present invention contemplates theuse of a strong base anion resin of high porosity, such as the Purolite501-P and equivalent resins, to filter silica particles from thesolution. These resins have a “filtration” functionality in view oftheir porosity, but also have the advantage of capturing silicaparticles on account of the anion-resin charge. Such resins can be usedas a first step in the treatment process, prior to removing the fluorideion in the solution by ion-exchange. It should be understood that thehigh porosity resins can be incorporated in disposable cartridges thatcan be replaced as necessary with fresh cartridges containing the resin.Alternatively, the high porosity resins can be disposed in resin vesselsthrough which the silica containing solution is passed; in such case,the resins can be regenerated with the same regenerant solution used toregenerate the HF removal resin.

Accordingly, the present invention has been described with some degreeof particularity directed to the exemplary embodiment of the presentinvention. It should be appreciated, though, that the present inventionis defined by the following claims construed in light of the prior artso that modifications or changes may be made to the exemplary embodimentof the present invention without departing from the inventive conceptscontained herein.

1. A method for removing fluorine gas from a gas stream from asemiconductor manufacturing process, comprising: providing a gas streamcomprising fluorine gas; providing an ion-exchange resin containingwater; contacting said gas stream comprising fluorine gas with the waterin said ion-exchange resin, thereby generating hydrofluoric acid;wherein fluoride ions in said hydrofluoric acid are exchanged forselected ions in said ion-exchange resin.
 2. A method according to claim1 wherein the ion-exchange resin is a weak-base anion exchange resin ora strong base anion exchange resin.
 3. A method according to claim 2wherein the ion-exchange resin is a crosslinked poly-4-vinylpyridineresin or derivative thereof.
 4. A method according to claim 1 whereinthe ion-exchange resin includes pyridine functional groups.
 5. A methodaccording to claim 4 wherein the ion-exchange resin is a crosslinkedpoly-4-vinylpyridine resin or derivative thereof.
 6. A method accordingto claim 1 wherein the generated hydrofluoric acid contains OF₂ or H₂O₂.7. A method according to claim 1 wherein contacting said gas streamcomprising fluorine gas with the water in said ion-exchange resin is acontinuous process.
 8. A method according to claim 1 wherein theion-exchange resin is doped with an electron donor catalyst.
 9. A methodaccording to claim 8 wherein the catalyst is palladium or titanium. 10.A method according to claim 1 further comprising regenerating theion-exchange resin with a regenerant solution and rinsing theion-exchange resin with a rinse solution.
 11. A method according toclaim 10 wherein the regenerant solution is ammonium hydroxide and therinse solution is de-ionized water.
 12. A method according to claim 1further comprising cooling the hydrofluoric acid.
 13. A method accordingto claim 12 wherein said ion-exchange resin and said hydrofluoric acidare contained in a vessel, and said hydrofluoric acid is cooled bycontacting said vessel with a heat exchanger apparatus.
 14. A methodaccording to claim 1 wherein the hydrofluoric acid has a pH between 5and 7.